'Concerning therefore the eating of things sacrificed to idols, we know that no idol is anything in the world, and that there is no God but one. For though there be that are called gods, whether in heaven or on earth, as there are gods many, and lords many, yet to us there is one God, the Father, of whom are all things, and we to him, and one Lord, Jesus Christ, through whom are all things, and we through him.'
Paul can agree with the Corinthians that no idol is really in the world in any meaningful way. They are nothing. And that there is no God but One. Many were called gods, both in the heavens and on earth. There were multitudes of them, both 'gods' and 'lords', the latter especially in the mystery religions. But they were nothing.
For there is only one God, the Father, and He is the source of all things. All is 'of Him'. And there is one Lord, Jesus Christ, Who also is the source of all things, all is 'through Him'. The very fact of including Jesus Christ in the argument demonstrates that Paul saw Him as truly God.
We note here that other 'gods' and 'lords' are equated. They are all at the same level. They are included in ‘those called gods'. And in contrast is the one God Who is both God and Lord. Thus when he speaks of 'One God' and 'One Lord' he is equating Father and Son in one Godhood. There is one God and one Lord revealed in twoness of relationship, and yet One in being and essence. God the Father is the source of all things, and supplies it through His Son, the Lord, Jesus Christ (Hebrews 1:1-3). There is but One God and One Lord, and the Father is both God and Lord, the latter made clear in the Old Testament, and Jesus Christ is both God and Lord. But the main point here is that they are the only God and Lord.
When speaking in the context of gods 'Lord' must signify the Old Testament name for God, Yahweh, the name above every name. That was always translated into Greek as 'Lord' (kurios) as here. And in Philippians 2:5-11 it is specifically applied to Jesus in that context. He has the name above every name. His name is 'Lord'. Thus the One God and Lord is here being contrasted, not with one another, but with the many 'gods and lords' and thus refers to the One God and Lord, Who incorporates the Father and Jesus Christ. They are the inter-communicating, inter-relational 'persona' within God. The Father reveals Himself in His Son.
To introduce the Lord Jesus Christ here as Lord when he is contrasting the One God with the many is to demonstrate His equal status in Godhood.
'And we to him -- and we through Him.' The first phrase stresses man's position as against God, as looking to Him and submissive and obedient to Him. The second stresses the redemptive factor, what we are now is through Him